In recent years bathtubs and other enclosures, either made of marble or having the appearance of marble, have become increasingly popular. Because, however, of the high expense of solid marble enclosures and fixtures, it has become the practice to fabricate these enclosures and fixtures from acrylic sheets. Ordinarily, these enclosures and fixtures are made of acrylic sheet produced by the continuous casting method. This procedure has the disadvantage, however, that pigments are frequently unevenly distributed within the sheet and there is the further problem that these acrylic sheets, once they are formed into the fixture, tend to deterioriate or become weakened in localized areas. Also due to the production techniques which are employed in fabricating enclosures and fixtures from these sheets, it is often difficult to repeat or match specific patterns which may be desired, and it is not infrequent that some localized areas do not match in color or in pattern with the result that a part of the sheet is discarded and wasted. Further, the continuous casting method being essentially a mass production system, it is impossible to produce a small batch to suit individual requirements.
In order to overcome the short comings, attempts have been made to apply patterns to acrylic sheets after thermoforming by spraying or applying a printed polyester or polystyrene film to the back of the formed acrylic sheet. Spraying to produce a desired pattern has, however, the disadvantage that it requires a high degree of skill on the part of the individual doing the spraying in order to produce a desired uniform appearance. Further, such spraying techniques cannot be applied to mass producing uniform designs, since the appearance of each article will necessarily vary somewhat. The application of printed polyester or polystyrene films to thermoformed acrylic sheets has the disadvantage that it is quite difficult to apply evenly the film to the intricate corners and undulations in the formed article thus resulting in a product with unsatisfactory appearance particularly at the corners and edges.
Accordingly, it is an object of the present invention to provide an inexpensive marble-patterned enclosure which is light in weight and high in rigidity and which has a marble pattern having an even appearance which can be reproduced exactly in any number of articles.
It is a further object of the present invention to provide a molded marble-patterned enclosure such as a bathtub or basin which can easily and inexpensively be fabricated in order to have the above-noted characteristics.
According to the present invention, an enclosure or fixture such as a bathtub or basin having a marble pattern is fabricated by applying a printed marble pattern to the back side of a generally flat unmolded sheet of acrylic followed by thermoforming the acrylic sheet into the desired configuration. A layer of opaque-colored primer, which comprises an unsaturated polyester containing 0.2 weight percent or more of a white pigment is then applied by spraying or by hand to the back of the acrylic sheet and then a layer of fiber glass reinforced polyester resin containing 20 to 40 weight percent fiber glass is applied to reinforce the structure.
One of the outstanding features of the present invention lies in applying the primer layer (FIG. 3--3) in addition to the FRP reinforcement layer (FIG. 3-4). Without the primer layer, applying FRP layer directly on the marble-patterned side of the sheet is liable to cause bubbles to form between the acrylic sheet and the layer. These bubbles and sometimes stray pieces of glass fiber are visible through the transparent acrylic sheet and render it exceedingly unsightly. Furthermore, the transfer-print ink is affected by the polyester resin of the FRP and the marble pattern frequently becomes deformed by bleeding of the ink or discolored.
Still another advantage of applying the primer layer according to the present invention is that it increases mechanical and physical strength of the enclosure as it brings about a stronger and more effective contact and adhesion between the sheet, pattern and FRP layer. Impact strength test by the falling ball method proves that impact strength is considerably improved by the present method over those without the primer layer. Also heat resistance test by hot water method, comprising abrupt filing of hot water in the enclosure and maintaining it for a long time, establishes that no peeling off of FRP layer, cracking of the sheet, discoloration or deformation of the marble pattern occurs.